1. Field of the Invention
The present invention relates to a content distribution method for distributing content data from a plurality of server apparatuses to a single client apparatus in a distributed manner, and to a program and an information processing apparatus for implementing the content distribution method.
2. Description of the Related Art
Recently, some video-on-demand (VOD) services using the Internet are available. However, since the volume of video content is large, large loads are placed on server computers and network circuits. Thus, some measures have been taken, such as degrading image quality to reduce the volume of content, providing a large number of mirror servers, or augmenting circuits near server computers or backbone circuits connected to Internet service providers (ISPs). However, users are not satisfied with low image quality of video content, and service providers and network administrators suffer huge cost of facilities for augmenting network circuits.
More recently, distributed storage environments, such as grid storage systems, are emerging. A grid storage system is a virtual storage system in which a large number of storage devices is connected via a network so that the storage devices as a whole look like a single large storage device. Grid storage systems are typically used in enterprise business environments, with each storage device located in a closed environment, such as a local area network (LAN).
Furthermore, a technology called BitTorrent, in which the scheme of grid storage is applied to an open environment such as a peer-to-peer (P2P) network, has been proposed. In an ordinary P2P network, data are exchanged on the basis of files. In contrast, in BitTorrent, a file is divided into blocks of a predetermined size, data is exchanged on the basis of the blocks, and the file is reconstructed from the blocks. BitTorrent can be considered as a grid storage system that is managed on a block basis. In BitTorrent, a plurality of host computers having a desired file is searched for over the Internet, and the plurality of host computers found by the search are simultaneously requested to send respectively different blocks of the file. This serves to achieve quick file transfer under a P2P network environment. In the case of a simple one-to-one P2P network, for example, when a host computer is connected by ADSL, the transfer rate is low since the rate of an upstream connection of an ADSL circuit is slow. Thus, the transfer rate is increased by retrieving blocks of a single file respectively from a plurality of host computers.
As methods for distributing loads of server computers and network circuits as described above, for example, according to Japanese Unexamined Patent Application Publication No. 2004-127168, packets of content data are distributed from a plurality of peers to a single peer in a P2P network so that loads of content distribution are distributed. As another example, according to Japanese Unexamined Patent Application Publication No. 2004-80307, a plurality of peers serves pieces of material data for producing programs so that the pieces of material data are available on a P2P network, and a receiving peer creates program content by retrieving the pieces of material data from the plurality of peers and combining the pieces of material data.